1. Field of the Invention
The present invention relates to antimicrobial composites which may be used, in particular, as wound coverings, dressings, cloths, and the like. By coating one side of a liquid-permeable material with an antimicrobial metal such as silver and laminating the resultant material to a material such as a liquid-absorbing nonwoven material with the metal coating facing the liquid-absorbing material, the abrasion of metal particles may be prevented while at the same time, the antimicrobial and disinfectant effect of the metal coating is retained.
2. Discussion of Background Information
Treating and healing bacterially contaminated skin and wounds, or infected skin and wounds is a major challenge to medicine and the natural sciences. Poorly healing and chronic wounds frequently become populated by a wide variety of microorganisms that considerably delay healing and sometimes even prevent healing altogether. Frequently, in the case of acute wounds that are caused by trauma, surgical intervention or even just simple injury, the penetration and infection by pathogenic microorganisms can, however, not completely be prevented.
Various possibilities are described for removing microorganisms from the contaminated or infected tissue of a wound and/or for killing the microorganisms. In addition to the oral administration of antibiotics, the removal of pathogenic microorganisms from a wound may be achieved, in accordance with the prior art, by the topical application of a disinfectant or an antibiotic. However, antiseptics and antibiotics are cytotoxic; in addition, many pathogenic strains have developed resistances to antibiotics.
An example of the known antimicrobial and/or prophylactic treatment of contaminated or infected wounds is the use of oxidants such as tincture of iodine, or of antiseptics such as ointments which contain silver sulfadiazine.
For a very long time, silver has been the agent of choice for treating infections, due to its broad bactericidal and fungicidal effect. In addition to its broad range of activity, silver is effective in minute, i.e., trace amounts (oligodynamic effect). Since the amounts of silver are so small, the tolerance is excellent. For example, silver aerosols, silver-containing solutions, ointments or tablets, etc. are widely used as antiseptics.
Silver-containing products are also used in the form of corresponding antimicrobially treated or impregnated wound dressings and wound care materials. The use of silver-containing zeolites, glasses and zirconyl phosphates, and also of silver in elemental or nanocrystalline form, is known as well.
Basically, there are two forms used for the administration of silver (ions), i.e., forms in which the silver ions are present in the product per se, and forms in which the ionic form of silver is generated by the oxidation of elemental silver. The first case essentially involves a dissolution or ion-exchange process. This makes the silver ions rapidly available, but the amount of silver ions in the preparation drops quickly as well. To provide a sufficient amount of silver to counteract this disadvantage is not without problems. For example, the cytotoxicity of silver ions limits the maximum acceptable amount thereof that can be used in a product.
Another disadvantage is that silver is deactivated by proteins, other complex-formers, or in the presence of ions that form scarcely-soluble silver salts. These conditions doubtlessly exist in wound fluids. In contrast, the release of silver from “elemental” silver (silver metal) is slower and occurs over a longer period, but takes place continuously. Accordingly, a sufficient amount of silver ions that is harmless to the user can always be released from the reservoir of elemental silver, the amount of silver ions depending on whether more or less of these ions can be released by equilibrium processes. The release of silver is, therefore, “as needed,” and the release of an effective quantity of silver is ensured.
An overview of known antimicrobial, silver-containing wound care materials is given in DE-A1-19958458.
A commercially available wound care product with antimicrobial properties is known under the name of Arglaes®. Its mode of action is based on “slow-release polymer” technology that causes a slow but constant release of silver ions in the moist milieu of the wound (Biomed. Mat., November 1995; Health Industry Today, 1 Nov. 1997, Vol. 58, No. 11).
DE-A1-19958458 discloses wound coverings comprising a synthetic polymer material which contains metal ion-containing zeolites.
Silver-containing glasses that have an antimicrobial effect are known from EP-A1-1116698 and EP-A1-1116700. These glasses are embedded in thermoplastic polymers that are used in a wide variety of forms for household and hygienic applications such as wallpaper, cutting boards, etc.
U.S. Pat. No. 5,753,251 and 5,681,575 describe antimicrobial coatings with so-called nanocrystalline silver that are formed on a medical product by depositing metals such as, e.g., silver from a gas phase. The antimicrobial effect is based on the release of ions, atoms, molecules or clusters from a disordered metal lattice when the silver is in contact with water or alcohol-based electrolytes. The corresponding product is known under the name Acticoat®. One of the disadvantages of this product is the visibly identifiable silver abrasion that causes a black discoloration of the covered skin area.
U.S. Pat. No. 2,934,066 describes a wound covering coated with metals, especially silver, which is reported to have a disinfecting effect.
The entire disclosures of the documents cited above, as well as those of all other documents mentioned in the present specification, are expressly incorporated by reference herein as if each of these documents in its entirety were part of the present specification.
Wound coverings comprising a non-woven material that is covered with a silver-coated polyethylene mesh are also known, e.g., Katomed®.
In all of the known disinfectant wound dressings which comprise a coating of elemental or nanocrystalline silver, the silver coating is intended to directly contact the wound. A disadvantage of these disinfecting materials is, therefore, that upon their contacting of the skin or wound they give rise to an abrasion and release of small particles of elemental silver. These particles form inclusions in the skin or wound, so-called granulomas, and can lead to complications during wound healing. Furthermore, due to the generated black discoloration, the aesthetic acceptance of corresponding products among users is very low.
It would be desirable to have available a material, e.g., a skin or wound dressing, which does not show the disadvantages of the known materials, but nevertheless shows antimicrobial activity.